In recent years, in order to achieve a higher breakdown voltage and lower loss of a semiconductor device, silicon carbide has increasingly been adopted as a material for forming a semiconductor device. Silicon carbide is a wide band-gap semiconductor greater in band gap than silicon conventionally widely used as a material for forming a semiconductor device. Therefore, by adopting silicon carbide as a material for forming a semiconductor device, a higher breakdown voltage, a lower on resistance of a semiconductor device and the like can be achieved. In addition, a semiconductor device adopting silicon carbide as a material is also more advantageous than a semiconductor device adopting silicon as a material in that deterioration in its characteristics at the time when it is used in an environment at a high temperature is less.
A semiconductor device containing silicon carbide as a constituent material is exemplified by a metal oxide semiconductor field effect transistor (MOSFET) or a bipolar device such as a diode (see M. Skowronski and S. Ha, “Degradation of hexagonal silicon-carbide-based bipolar devices,” Journal of Applied Physics, (United States), AIP Publishing LLC, Jan. 13, 2006, Vol. 99, 011101 (1 to 24) (NPD 1)). The MOSFET is a unipolar device in which migration of one type of carriers between a source electrode and a drain electrode is controlled with a prescribed threshold voltage being defined as the boundary.